Instrument tees are well known in the art for providing a mounting platform in pipelines for instruments such as thermocouples, pressure transducers, pH meters, flowmeters, and the like. As a practical matter, however, standard instruments come in many sizes and connections, and sometimes the instrument connection may be larger than the pipe or tubing line into which the instrument is mounted. This may be particularly true of small-scale processes prevalent in the pharmaceutical and biotech industries. Instrument tees used in such situations frequently resemble the “bucket-type” instrument tee 10 illustrated in FIGS. 1 and 2.
Instrument tee 10, shown in plan view in FIG. 1, comprises a body member 12 having an inlet 16 and an outlet 18 for providing a flow path through the body, and a concave surface that forms a cup 14 in fluid communication with the flow path for providing fluid access to the instrument. Cup 14 has a central axis L Inlet 16 and outlet 18 (and the resulting flow path) are aligned in a straight line L that intersects with central axis I. It should be noted that the term “fluid” as used herein refers to any process material that is of a sufficiently flowable nature that makes it appropriate for processing within a pipeline in which the instrument tee is mounted. Such a fluid may include but is not limited to a liquid, a gas, a liquid/gas mixture (such as a vapor with entrained condensate), a liquid/solid mixture (such as a dispersion or slurry), and a gas/solid mixture (for example, fluidized particles in a pneumatic conveying operation).
In many pharmaceutical or biotech processes, it is important to be able to periodically drain the system completely, often because the fluid within the piping is highly valuable and sought to be recovered or because it is necessary to completely clean the piping between batches to avoid cross-contamination. Although instrument tee 10 is capable of draining completely when the tee is mounted in a pipeline with central axis I aligned vertically, the piping configuration may not always permit a vertical installation. FIG. 2, a cross-section of tee 10 shown in FIG. 1, illustrates what happens inside instrument tee 10, when the tee has been installed in a position that is rolled along axis L so that central axis/is at a sufficiently large angle relative to vertical V. Because of the geometric configuration of region 22 pooling of material 24 occurs. The pooled material may be a liquid, such as process liquid or condensate, or a solid, such as particulate or biological material settled out of a slurry or left behind by a fluidizing gas.
In addition to the loss of product and potential contamination from batch to batch that such pooling may cause, the pooled material may also be prone to formation of living contaminants such as bacteria, mold, and the like, in some systems. Also, in liquid/solid or gas/solid systems, region 22 may be prone to build-up of sediment that is difficult to clean or remove, even upon opening the tee and removing the instrument to get access to cup 14 for a thorough cleaning. For any of these reasons, pooling may be unacceptable in many types of installations, and therefore design of piping systems and fittings to prevent pooling is desirable.
It is also important for the proper operation of an instrument tee, that the instrument tee becomes sufficiently filled and completely refreshed with process fluid so that the fluid reaches an interface with the instrument to allow the instrument to get a true reading of the process conditions. In a piping system that has been drained of any process liquid, for example, air (or other blanketing gas, referred to generally herein as “air”) typically fills the piping, unless the system has been put under vacuum. It is important in many cases to avoid the formation of air pockets when filling or re-filling a piping system with process liquid. Furthermore, in other types of systems and even once a liquid system is filled, it is important to avoid stagnant pockets of fluid which may form in the cup above the flow path, depending upon the fluid dynamics of the system.
Thus, for example, instrument tee 10 may be prone to development of an air pocket or stagnant region above minimum fluid line F as shown in FIG. 2. It should be understood that the “minimum fluid line” may not just denote a liquid/gas interface, but can also denote the interface between a moving region and a stagnant region. If the probe or other sensing interface of the instrument mounted in the mounting tee does not extend down below line F and an air pocket or other stagnant region is present above line F, this is likely to adversely affect the readings provided by the instrument. In other cases, the mere presence of air in the system may pose unacceptable risks to the purity of the process materials. Accordingly, it is also desirable to design piping systems and fittings to avoid formation of air pockets or otherwise stagnant regions.